JP7226262B2 - engine controller - Google Patents

Description

The technology disclosed herein relates to an engine control device.

Patent Literature 1 describes an engine that burns gasoline fuel by compression ignition. In this engine, the combustion timing of compression self-ignition combustion is such that the relationship between the crank angle at which the mass combustion ratio is 50% and the crank angle period at which the mass combustion ratio is from 10% to 50% is a predetermined relationship. and control the burn rate. As a result, this engine improves thermal efficiency, improves combustion stability, and reduces combustion noise.

JP 2001-355484 A

The applicant of the present application has proposed SPCCI (SPark Controlled Compression Ignition) combustion as compression self-ignition combustion. SPCCI combustion is combustion in which SI (Spark Ignition) combustion and CI (Compression Ignition) combustion are combined. SI combustion is combustion with flame propagation initiated by forced ignition of the air-fuel mixture in the combustion chamber. CI combustion is combustion initiated by compression autoignition of the air-fuel mixture in the combustion chamber. In SPCCI combustion, the air-fuel mixture in the combustion chamber is forcibly ignited to start combustion by flame propagation. is a form that burns by compression ignition. In the following description, SPCCI combustion may be referred to as partial self-ignition combustion.

In SI combustion and SPCCI combustion, in which combustion starts when a spark plug ignites an air-fuel mixture, the combustion timing can be adjusted by adjusting the ignition timing of the spark plug. By advancing the ignition timing, if the mixture burns on the advance side, the thermal efficiency of the engine is improved.

However, in SPCCI combustion, when the ignition timing is advanced, the proportion of CI combustion in SPCCI combustion increases. As the proportion of CI combustion increases, combustion noise increases relatively. In SPCCI combustion, combustion noise increases as the ignition timing advances. Further, if the ignition timing is advanced too much, abnormal combustion may occur, which may reduce the reliability of the engine. An engine that performs SPCCI combustion, unlike an engine that performs SI combustion, must set ignition timing in consideration of combustion noise and/or reliability.

The technique disclosed herein appropriately sets the ignition timing of an engine that performs SPCCI combustion.

The applicant of the present application focused on the fact that mfb50 (mass fraction burned: crank angle at which mass fraction burned is 50%) and cplf (cylinder pressure level filtered: combustion noise index) are highly correlated. The combustion noise index is the frequency spectrum of pressure changes in the combustion chamber.

The applicant of the present application set the target mfb50 based on the relationship between mfb50 and cplf, and completed the logic for setting the ignition timing to achieve the target mfb50. In this logic, the target mfb50 is set based on the most retarded position of mfb50 when the air-fuel mixture undergoes partial self-ignition combustion.

Combustion such that mfb50 is too slow, the mixture does not initiate combustion by autoignition, but only by flame propagation. When the air-fuel mixture undergoes partial self-ignition combustion, mfb50 is relatively positioned on the advance side. The most retarded position of mfb 50 when the air-fuel mixture performs partial self-ignition combustion is determined according to the state of the combustion chamber. The most retarded position of mfb 50 changes as conditions within the combustion chamber change.

The most retarded position of mfb50 can be estimated based on a mixture autoignition model. The autoignition model may be, for example, an equation that models the autoignition of the air-fuel mixture in the combustion chamber based on the Arrhenius equation.

When the most retarded position of mfb 50 is determined, mfb 50 can be advanced based on the most retarded position as long as cplf does not exceed the limit value. The mfb50 advanced to the limit is the target mfb50.

In order to determine the advance limit of mfb50, cplf during combustion at the most retarded position of mfb50 is estimated. Combustion at the most retarded position of mfb50 is combustion with a small amount of CI combustion in partial self-ignition combustion. The cplf of the partial self-ignition combustion can be regarded as the same or substantially the same as the cplf of the SI combustion. Therefore, cplf during combustion at the most retarded position of mfb50 may be estimated on the assumption that the air-fuel mixture undergoes SI combustion instead of partial self-ignition combustion. The cplf of SI combustion can be estimated based on the combustion waveform of SI combustion. The combustion waveform for SI combustion can be obtained, for example, by simulation or from actual combustion data.

The advance limit of mfb50 can be calculated based on an estimated value of cplf during combustion at the most retarded position of mfb50, a limit value of cplf, and a predetermined relationship between mfb50 and cplf.

Once the advance limit of mfb50, that is, the target value of mfb50 is calculated, the ignition timing that provides the target mfb50 is set. When the ignition unit ignites at the set ignition timing, the air-fuel mixture in the combustion chamber undergoes partial self-ignition combustion such that mfb50 becomes the target mfb50. This ensures that cplf does not exceed the limit. As a result, an increase in combustion noise and a decrease in reliability of the engine can be suppressed. In addition, since mfb50 is advanced as much as possible, fuel efficiency can be improved.

If the ignition timing is controlled according to the logic described above, combustion noise can be suppressed and fuel efficiency can be improved when the engine operating condition is constant or substantially constant. However, the inventors of the present invention have found that, even if the ignition timing is controlled by the logic described above, combustion noise increases during a transient period in which the operating state of the engine changes.

As a result of repeated studies on this technical problem, the inventors of the present application have found that there is a problem in setting the target value of cplf.

As described above, the target value of cplf is a value set from the limit value of cplf and is an index of the advance limit of mfb50. In the above logic, the target value of cplf is set to a value smaller than the limit value of cplf so that cplf does not exceed the limit value in consideration of combustion fluctuation (variation in combustion). Specifically, the standard deviation of cplf based on accumulated cplf measurement data is used to set the target value of cplf so that the limit value of cplf is, for example, 3σ. Note that the cplf measurement data is subjected to low-pass filter processing for the purpose of noise removal and the like.

Here, the magnitude of variation in SPCCI combustion can be represented by the standard deviation of mfb50. The standard deviation of mfb50 varies with the position of mfb50. If mfb50 is on the retard side, the standard deviation of mfb50 is large, and if mfb50 is on the advance side, the standard deviation of mfb50 is small. Since the degree of variation in cplf is affected by the standard deviation of mfb50, the standard deviation of cplf varies depending on the operating conditions of the engine.

When the engine is steady, the operating state is constant or almost constant over time. Therefore, the combustion fluctuation does not change or hardly changes. The standard deviation of cplf also does not change or hardly changes. By determining the target value of cplf from the limit value of cplf using the standard deviation of cplf based on the measurement data, it is possible to prevent cplf from exceeding the limit value when the engine is stationary.

However, when the operating state of the engine changes over time, the combustion fluctuation also changes from moment to moment as the operating condition of the engine changes from moment to moment. The standard deviation of cplf also changes moment by moment during engine transients. The standard deviation of cplf based on low-pass filtered measurement data changes slowly over time. If the target value of cplf is determined using the standard deviation of cplf based on measurement data during engine transients, the target value of cplf deviates greatly from the operating state of the engine. As a result, cplf exceeds the limit value, that is, combustion noise increases.

Therefore, the inventors of the present application used a model to predict the standard deviation of cplf and determined the target value of cplf using the predicted standard deviation of cplf.

Specifically, the technology disclosed herein relates to an engine control device. This control device
an ignition unit facing a combustion chamber of an engine mounted on an automobile and igniting an air-fuel mixture in the combustion chamber based on an ignition signal;
a measurement unit that outputs measurement signals of parameters related to the operation of the engine;
A control unit that receives a measurement signal from the measurement unit and performs calculation, and outputs an ignition signal based on the calculation result to the ignition unit,
The measurement unit includes a cylinder pressure sensor that outputs a measurement signal corresponding to pressure changes in the combustion chamber,
The control unit causes the ignition unit to perform partial self-ignition combustion in which the remaining mixture burns by self-ignition after a part of the mixture starts combustion with flame propagation by ignition of the ignition unit. outputting the ignition signal;
The control unit
a target value setting unit that sets a target value of the cplf from a limit value of the combustion noise index (cplf) set based on the measurement signal of the measurement unit;
an mfb50 estimating unit that estimates the most retarded position of the crank angle (mfb50 ) at which the mass combustion ratio is 50% when the air-fuel mixture performs partial self-ignition combustion based on the self-ignition model of the air-fuel mixture;
Combustion that satisfies the target value of cplf based on the target value of cplf set by the target value setting unit, the most retarded position of mfb50 estimated by the mfb50 estimation unit, and the predetermined relationship between mfb50 and cplf a target mfb50 calculator that calculates the mfb50 of
an ignition timing setting unit that sets an ignition timing that becomes the target mfb50 calculated by the target mfb50 calculation unit and outputs an ignition signal corresponding to the set ignition timing;
The target value setting unit
a first sigma calculator that calculates the standard deviation of the actual cplf based on the measurement signal of the in-cylinder pressure sensor;
Based on the mfb50-sigma model representing the relationship between mfb50 and mfb50 variation and the relationship between mfb50 and cplf, the standard deviation of cplf at the cplf limit from the mfb50 variation corresponding to the cplf limit a second sigma calculator that calculates
a correction unit that corrects the standard deviation of cplf calculated by the first sigma calculation unit based on the standard deviation of cplf calculated by the second sigma calculation unit;
The target value setting unit sets the target value of cplf based on the limit value of cplf and the corrected standard deviation of cplf so that cplf does not exceed the limit value.

According to the above configuration, the target value setting section first sets the limit value of cplf based on the measurement signal from the measurement section. The limit value of cplf is determined based on, for example, the running speed of the vehicle and/or the number of revolutions and load of the engine in consideration of marketability. The measurement unit outputs measurement signals of parameters related to the running speed of the vehicle and/or the number of revolutions and load of the engine. The target value setting unit also sets the target value of cplf from the limit value of cplf. As will be described later, the target value setting section sets the target value of cplf so that cplf does not exceed the limit value in consideration of combustion fluctuations.

The target mfb50 calculator calculates a partial self that satisfies the target value of cplf based on the most retarded position of mfb50 estimated by the mfb50 estimator, the target value of cplf, and a predetermined relationship between mfb50 and cplf. Calculate mfb50 for ignition combustion. Then, the ignition timing setting unit sets the ignition timing to achieve the target mfb50, and outputs an ignition signal corresponding to the set ignition timing. This results in partial self-ignition combustion of the air-fuel mixture in the combustion chamber. The mfb50 of the partial self-ignition combustion becomes the target mfb50. By advancing mfb50 to the extent possible while suppressing an increase in combustion noise, the fuel efficiency of the engine is improved.

In the control device for the engine configured as described above, the target value setting unit determines the target value of cplf from the standard deviation of cplf calculated by the first sigma calculating unit and the standard deviation of cplf calculated by the second sigma calculating unit. set. Thereby, the target value setting unit can appropriately set the target value of cplf.

Specifically, the first sigma calculator calculates the standard deviation of the actual cplf based on the measurement signal of the in-cylinder pressure sensor. The first sigma calculator accumulates the measurement signal of the in-cylinder pressure sensor, and calculates the standard deviation of cplf from the accumulated information on the pressure change in the combustion chamber.

The second sigma calculator calculates the standard deviation of cplf at the cplf limits based on the mfb50-sigma model and the relationship between mfb50 and cplf. The second sigma calculator predicts the standard deviation of cplf using a model of combustion variation. Even during engine transition, the second sigma calculator can calculate the standard deviation of cplf without delay.

The correction unit corrects the standard deviation of cplf calculated by the first sigma calculation unit based on the standard deviation of cplf calculated by the second sigma calculation unit. The corrector feed-forwards the standard deviation of cplf calculated using the model to the standard deviation of cplf calculated based on the measurement signal.

The target value setting unit sets the target value of cplf based on the limit value of cplf and the corrected standard deviation of cplf so that cplf does not exceed the limit value. As described above, the standard deviation of cplf calculated based on the measurement signal is corrected by the standard deviation of cplf calculated using a model related to combustion fluctuation. The corrected cplf standard deviation represents the cplf variation during engine transients. The target value setting unit can use the corrected standard deviation of cplf to appropriately set the target value of cplf during engine transients.

For example, when the driver depresses the accelerator pedal, combustion noise is prevented from increasing significantly. Further, even when the engine is in transition, mfb50 is advanced to the extent possible, so the fuel efficiency of the engine is improved.

The correction unit calculates the difference between the first standard deviation without low-pass filtering and the second standard deviation after low-pass filtering with respect to the standard deviation of cplf calculated by the second sigma calculation unit,
The correction unit may add the difference between the first standard deviation and the second standard deviation to the standard deviation of cplf calculated by the first sigma calculation unit.

The first standard deviation does not include lag during engine transients because it does not low-pass filter the standard deviation of cplf calculated using the model. The second standard deviation contains lag during engine transients due to low pass filtering of the standard deviation of cplf calculated using the model. During engine transients, the difference between the first standard deviation and the second standard deviation is large. On the other hand, when the engine is stationary, there is no difference between the first standard deviation and the second standard deviation, or the difference is small.

The correction unit adds the difference between the first standard deviation and the second standard deviation to the standard deviation of cplf calculated by the first sigma calculation unit. As described above, when the engine is stationary, there is no difference between the first standard deviation and the second standard deviation, or the difference is small. The standard deviation of the signal-based cplf is not or hardly corrected. When the engine is stationary, the target value setting unit determines the target value from the limit value of cplf based on the standard deviation of cplf based on the measurement signal.

When the engine is in transition, the difference between the first standard deviation and the second standard deviation is large, so the correction unit greatly corrects the standard deviation of cplf based on the measurement signal. During engine transients, the target value setting unit determines the target value from the cplf limits based on the corrected standard deviation of cplf.

The target value setting section does not determine whether the engine is in a steady state or in a transient state. While the control logic of the engine is simplified, both the suppression of combustion noise and the improvement of fuel efficiency are achieved both in the steady state and in the transient state of the engine.

The second sigma calculator,
a standard deviation of cplf corresponding to 1 sigma of mfb50 corresponding to the cplf limit;
a standard deviation of cplf corresponding to 2 sigma of mfb50 corresponding to the cplf limit;
a standard deviation of cplf corresponding to the 3 sigma of mfb50 corresponding to the limit of cplf;
may be used as the standard deviation of cplf at the limit value of cplf.

In this way, the second sigma calculator can accurately calculate the standard deviation of cplf at the limit value of cplf based on the degree of variation of mfb50 when the operating state of the engine changes from moment to moment.

The control unit determines whether partial self-ignition combustion of the air-fuel mixture has occurred based on the measurement signal of the cylinder pressure sensor, and if partial self-ignition combustion has occurred, measurement of the cylinder pressure sensor is performed. The actual cplf measured based on the signal may be used to correct the relationship between mfb50 and cplf.

By doing so, the relationship between mfb50 and cplf is corrected based on the actually measured combustion state of the air-fuel mixture. The control unit can more appropriately set the target mfb50 based on the corrected relationship between mfb50 and cplf.

The mfb50 estimation unit
Self-ignition model of air-fuel mixture T _CI ^A ×P _CI ^B ×(O2_rate) ^C ×φ ^D /time=1
(However, T _CI is the temperature in the combustion chamber when the air-fuel mixture self-ignites, _PCI is the pressure in the combustion chamber when the air-fuel mixture self-ignites, O2_rate is the oxygen concentration in the combustion chamber, and φ is the equivalence ratio of the air-fuel mixture. , time is time, A, B, C, and D are constants), and
Relational expression of pressure change in the combustion chamber P _CI = P _BDC × (V _BDC /V _CI ) ^κ + Q × (κ - 1) / V _CI
(However, P _BDC is the pressure in the combustion chamber at intake bottom dead center, V _BDC is the volume in the combustion chamber at intake bottom dead center, V _CI is the volume in the combustion chamber when the mixture self-ignites, and Q is the mixture κ is the specific heat ratio of the air-fuel mixture)
, the volume V _CI of the combustion chamber at the time when the air-fuel mixture in the combustion chamber starts self-ignition is estimated, and the most retarded position of mfb 50 is estimated from the estimated volume V _CI .

The mfb50 estimator can accurately estimate the most retarded position of mfb50 when the air-fuel mixture performs partial self-ignition combustion based on the air-fuel mixture autoignition model.

As described above, the engine control device can appropriately set the ignition timing of the engine that performs SPCCI combustion.

FIG. 1 is a diagram illustrating the configuration of an engine. FIG. 2 is a diagram illustrating the configuration of the combustion chamber, the upper diagram being a plan view equivalent of the combustion chamber, and the lower diagram being a sectional view taken along line II-II. FIG. 3 is a block diagram illustrating the configuration of an engine control device. FIG. 4 is a diagram illustrating waveforms of SPCCI combustion. FIG. 5 is a diagram illustrating a control map of the engine when it is warm. FIG. 6 is a flowchart illustrating basic engine control. FIG. 7 is a diagram illustrating the relationship between mfb50 and combustion noise index in SPCCI combustion. FIG. 8 is a block diagram illustrating the configuration of an engine control device for setting ignition timing. FIG. 9 is a diagram for explaining a method of setting the target mfb50. The upper diagram illustrates the relationship between mfb50 and the combustion noise index in SPCCI combustion, and the lower diagram illustrates the volume ratio of the combustion chamber and the combustion noise index. It is a figure which illustrates the relationship with. The upper diagram in FIG. 10 is a diagram illustrating the waveform of SPCCI combustion, and the lower diagram is a diagram illustrating changes in heat release. FIG. 11 is a diagram for explaining a model correction procedure using a measurement signal of an in-cylinder pressure sensor. FIG. 12 is a flowchart illustrating control related to ignition. FIG. 13 is a block diagram illustrating the configuration of a cplf target value setting unit. FIG. 14 is a diagram for explaining a method of setting the target mfb50 when the engine is in transition. FIG. 15 is a diagram illustrating the difference in standard deviation of cplf with and without low-pass filtering. FIG. 16 is a diagram illustrating the calculation procedure in step S5 of the flow of FIG.

An embodiment of an engine control device will be described in detail below with reference to the drawings. The following description is an example of an engine and a control system for the engine.

FIG. 1 is a diagram illustrating the configuration of a compression ignition engine system. FIG. 2 is a diagram illustrating the configuration of the combustion chamber of the engine. Note that the intake side in FIG. 1 is on the left side of the paper, and the exhaust side is on the right side of the paper. The intake side in FIG. 2 is on the right side of the paper, and the exhaust side is on the left side of the paper. FIG. 3 is a block diagram illustrating the configuration of an engine control device.

The engine 1 is a four-stroke engine that operates by repeating an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in a combustion chamber 17 . The engine 1 is installed in a four-wheeled automobile. The automobile runs as the engine 1 operates. The fuel of the engine 1 is gasoline in this configuration example. The fuel may be liquid fuel containing at least gasoline. The fuel may be gasoline, including, for example, bioethanol.

(Engine configuration)
The engine 1 has a cylinder block 12 and a cylinder head 13 mounted thereon. A plurality of cylinders 11 are formed inside the cylinder block 12 . 1 and 2 only one cylinder 11 is shown. The engine 1 is a multi-cylinder engine.

A piston 3 is slidably inserted in each cylinder 11 . Piston 3 is connected to crankshaft 15 via connecting rod 14 . Piston 3 defines combustion chamber 17 together with cylinder 11 and cylinder head 13 . Incidentally, the term "combustion chamber" may be used in a broad sense. In other words, the "combustion chamber" may mean the space formed by the piston 3, the cylinder 11 and the cylinder head 13 regardless of the position of the piston 3.

The lower surface of the cylinder head 13, that is, the ceiling surface of the combustion chamber 17 is composed of an inclined surface 1311 and an inclined surface 1312 as shown in the lower diagram of FIG. The inclined surface 1311 slopes upward from the intake side toward the injection axis X2 of the injector 6, which will be described later. The inclined surface 1312 slopes upward from the exhaust side toward the injection axis X2. The ceiling surface of the combustion chamber 17 has a so-called pent roof shape.

The upper surface of the piston 3 protrudes toward the ceiling surface of the combustion chamber 17 . A cavity 31 is formed in the upper surface of the piston 3 . A cavity 31 is recessed from the upper surface of the piston 3 . The cavity 31 has a shallow plate shape in this configuration example. The center of the cavity 31 is shifted from the center axis X1 of the cylinder 11 toward the exhaust side.

The geometric compression ratio of the engine 1 is set to 10 or more and 30 or less. As will be described later, the engine 1 performs SPCCI combustion, which is a combination of SI combustion and CI combustion, in some operating ranges. SPCCI combustion utilizes the heat generation and pressure increase due to SI combustion to control CI combustion. The engine 1 is a compression ignition engine. However, this engine 1 does not need to increase the temperature of the combustion chamber 17 when the piston 3 reaches the compression top dead center (that is, the compression end temperature). The engine 1 can have a relatively low geometric compression ratio. A lower geometric compression ratio favors lower cooling losses and lower mechanical losses. The geometric compression ratio of the engine 1 is 14 to 17 for regular specifications (low octane fuel with an octane number of about 91) and 15 for high octane specifications (high octane fuel with an octane number of about 96). ~18 may be used.

An intake port 18 is formed in the cylinder head 13 for each cylinder 11 . Although not shown, the intake port 18 has a first intake port and a second intake port. The intake port 18 communicates with the combustion chamber 17 . Although detailed illustration is omitted, the intake port 18 is a so-called tumble port. That is, the intake port 18 has a shape that forms a tumble flow in the combustion chamber 17 .

An intake valve 21 is arranged in the intake port 18 . The intake valve 21 opens and closes between the combustion chamber 17 and the intake port 18 . The intake valve 21 is opened and closed at a predetermined timing by a valve mechanism. The valve mechanism may be a variable valve mechanism that varies valve timing and/or valve lift. In this configuration example, the variable valve mechanism has an electric intake S-VT (Sequential-Valve Timing) 23, as shown in FIG. The electric intake S-VT 23 continuously changes the rotation phase of the intake camshaft within a predetermined angle range. The opening timing and closing timing of the intake valve 21 continuously change. The intake valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

The cylinder head 13 is also formed with an exhaust port 19 for each cylinder 11 . The exhaust port 19 also has a first exhaust port and a second exhaust port. The exhaust port 19 communicates with the combustion chamber 17 .

An exhaust valve 22 is arranged in the exhaust port 19 . The exhaust valve 22 opens and closes between the combustion chamber 17 and the exhaust port 19 . The exhaust valve 22 is opened and closed at a predetermined timing by a valve mechanism. This valve mechanism may be a variable valve mechanism that varies valve timing and/or valve lift. In this configuration example, the variable valve mechanism has an electric exhaust S-VT 24, as shown in FIG. The electric exhaust S-VT 24 continuously changes the rotation phase of the exhaust camshaft within a predetermined angle range. The opening timing and closing timing of the exhaust valve 22 continuously change. The exhaust valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

The electric intake S-VT 23 and the electric exhaust S-VT 24 adjust the length of the overlap period during which both the intake valve 21 and the exhaust valve 22 are open. By increasing the length of the overlap period, residual gases in the combustion chamber 17 can be scavenged. Also, internal EGR (Exhaust Gas Recirculation) gas can be introduced into the combustion chamber 17 by adjusting the length of the overlap period. The internal EGR system is composed of an electric intake S-VT 23 and an electric exhaust S-VT 24 . It should be noted that the internal EGR system is not necessarily composed of S-VT.

An injector 6 is attached to the cylinder head 13 for each cylinder 11 . Injector 6 injects fuel directly into combustion chamber 17 . The injector 6 is an example of a fuel injection section. The injector 6 is arranged in the valley of the pent roof where the inclined surfaces 1311 and 1312 intersect. As shown in FIG. 2, the injection axis X2 of the injector 6 is positioned closer to the exhaust side than the center axis X1 of the cylinder 11. As shown in FIG. The injection axis X2 of the injector 6 is parallel to the central axis X1. The injection axis X2 of the injector 6 and the center of the cavity 31 are aligned. The injector 6 faces the cavity 31 . Note that the injection axis X2 of the injector 6 may coincide with the central axis X1 of the cylinder 11 . In that configuration, the injection axis X2 of the injector 6 and the center of the cavity 31 may coincide.

Although detailed illustration is omitted, the injector 6 is configured by a multi-orifice fuel injection valve having a plurality of orifices. The injector 6 injects the fuel so that the fuel spray spreads radially from the center of the combustion chamber 17, as indicated by the two-dot chain line in FIG. In this configuration example, the injector 6 has ten injection holes, and the injection holes are arranged at equal angles in the circumferential direction.

A fuel supply system 61 is connected to the injector 6 . The fuel supply system 61 includes a fuel tank 63 configured to store fuel, and a fuel supply path 62 connecting the fuel tank 63 and the injector 6 to each other. A fuel pump 65 and a common rail 64 are interposed in the fuel supply path 62 . A fuel pump 65 pumps fuel to the common rail 64 . The fuel pump 65 is a plunger pump driven by the crankshaft 15 in this configuration example. The common rail 64 stores fuel pressure-fed from the fuel pump 65 at high fuel pressure. When the injector 6 opens, the fuel stored in the common rail 64 is injected into the combustion chamber 17 from the injection port of the injector 6 . The fuel supply system 61 is capable of supplying high pressure fuel of 30 MPa or higher to the injector 6 . The pressure of fuel supplied to the injector 6 may be changed according to the operating state of the engine 1 . Note that the configuration of the fuel supply system 61 is not limited to the configuration described above.

A spark plug 25 is attached to the cylinder head 13 for each cylinder 11 . A spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17 . The spark plug 25 is disposed on the intake side of the central axis X1 of the cylinder 11 in this configuration example. A spark plug 25 is positioned between the two intake ports 18 . The spark plug 25 is attached to the cylinder head 13 so as to be tilted from top to bottom toward the center of the combustion chamber 17 . The electrode of the spark plug 25 faces the inside of the combustion chamber 17 and is positioned near the ceiling surface of the combustion chamber 17, as shown in FIG. Note that the spark plug 25 may be arranged on the exhaust side of the central axis X1 of the cylinder 11 . Further, the spark plug 25 may be arranged on the center axis X1 of the cylinder 11. FIG.

An intake passage 40 is connected to one side surface of the engine 1 . The intake passage 40 communicates with the intake port 18 of each cylinder 11 . Gas introduced into the combustion chamber 17 flows through the intake passage 40 . An air cleaner 41 is arranged at the upstream end of the intake passage 40 . The air cleaner 41 filters fresh air. A surge tank 42 is arranged near the downstream end of the intake passage 40 . The intake passage 40 downstream of the surge tank 42 constitutes an independent passage that branches for each cylinder 11 . A downstream end of the independent passage is connected to the intake port 18 of each cylinder 11 .

A throttle valve 43 is arranged between the air cleaner 41 and the surge tank 42 in the intake passage 40 . The throttle valve 43 adjusts the amount of fresh air introduced into the combustion chamber 17 by adjusting the opening of the valve.

A supercharger 44 is also arranged in the intake passage 40 downstream of the throttle valve 43 . The supercharger 44 supercharges the gas introduced into the combustion chamber 17 . In this configuration example, the supercharger 44 is a mechanical supercharger driven by the engine 1 . The mechanical supercharger 44 may be of the Roots, Lysholm, vane, or centrifugal type.

An electromagnetic clutch 45 is interposed between the supercharger 44 and the engine 1 . Between the supercharger 44 and the engine 1 , the electromagnetic clutch 45 transmits driving force from the engine 1 to the supercharger 44 or cuts off transmission of the driving force. As will be described later, the ECU 10 switches between connection and disconnection of the electromagnetic clutch 45 to switch the supercharger 44 between on and off.

An intercooler 46 is arranged downstream of the supercharger 44 in the intake passage 40 . Intercooler 46 cools the gas compressed in supercharger 44 . The intercooler 46 may be configured to be water-cooled or oil-cooled, for example.

A bypass passage 47 is connected to the intake passage 40 . The bypass passage 47 connects the upstream portion of the supercharger 44 and the downstream portion of the intercooler 46 in the intake passage 40 so as to bypass the supercharger 44 and the intercooler 46 . An air bypass valve 48 is arranged in the bypass passage 47 . The air bypass valve 48 adjusts the flow rate of gas flowing through the bypass passage 47 .

The ECU 10 fully opens the air bypass valve 48 when the turbocharger 44 is turned off (that is, when the electromagnetic clutch 45 is disconnected). Gas flowing through the intake passage 40 bypasses the supercharger 44 and is introduced into the combustion chamber 17 of the engine 1 . The engine 1 operates in a non-supercharged state, that is, in a naturally aspirated state.

When the supercharger 44 is turned on, the engine 1 operates in a supercharged state. The ECU 10 adjusts the opening degree of the air bypass valve 48 when the supercharger 44 is turned on (that is, when the electromagnetic clutch 45 is connected). Part of the gas that has passed through the supercharger 44 flows back upstream of the supercharger 44 through the bypass passage 47 . When the ECU 10 adjusts the opening of the air bypass valve 48, the boost pressure of the gas introduced into the combustion chamber 17 changes. It should be noted that the term "supercharging" refers to the time when the pressure in the surge tank 42 exceeds the atmospheric pressure, and the term "non-supercharging" refers to the time when the pressure in the surge tank 42 falls below the atmospheric pressure. good too.

In this configuration example, a supercharging system 49 is configured by the supercharger 44 , the bypass passage 47 and the air bypass valve 48 .

The engine 1 has a swirl generator in the combustion chamber 17 that generates a swirl flow. The swirl flow flows as indicated by white arrows in FIG. The swirl generator has a swirl control valve 56 attached to the intake passage 40 . Although not shown in detail, the swirl control valve 56 is in the secondary passage of the primary passage leading to one of the two intake ports 18 and the secondary passage leading to the other intake port 18. are arranged. The swirl control valve 56 is an opening control valve capable of narrowing the cross section of the secondary passage. If the opening of the swirl control valve 56 is small, the amount of intake air entering the combustion chamber 17 from one intake port 18 is relatively large, and the amount of intake air entering the combustion chamber 17 from the other intake port 18 is relatively small. , the swirl flow in the combustion chamber 17 becomes stronger. When the opening of the swirl control valve 56 is large, the amount of intake air entering the combustion chamber 17 from each of the two intake ports 18 becomes substantially equal, so the swirl flow in the combustion chamber 17 weakens. When the swirl control valve 56 is fully opened, no swirl flow occurs.

An exhaust passage 50 is connected to the other side surface of the engine 1 . The exhaust passage 50 communicates with the exhaust port 19 of each cylinder 11 . The exhaust passage 50 is a passage through which the exhaust gas discharged from the combustion chamber 17 flows. An upstream portion of the exhaust passage 50 constitutes an independent passage that branches for each cylinder 11, although detailed illustration is omitted. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11 .

An exhaust gas purification system having a plurality of catalytic converters is arranged in the exhaust passage 50 . Although not shown, the exhaust gas purification system is installed in the engine room. The upstream catalytic converter has a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512 . The downstream catalytic converter has a three-way catalyst 513 . It should be noted that the exhaust gas purification system is not limited to the configuration of the illustrated example. For example, GPF may be omitted. Also, the catalytic converter is not limited to having a three-way catalyst. Furthermore, the order in which the three-way catalyst and GPF are arranged may be changed as appropriate.

An EGR passage 52 that constitutes an external EGR system is connected between the intake passage 40 and the exhaust passage 50 . The EGR passage 52 is a passage for recirculating part of the exhaust gas to the intake passage 40 . The upstream end of the EGR passage 52 is connected between the upstream and downstream catalytic converters in the exhaust passage 50 . A downstream end of the EGR passage 52 is connected to an upstream portion of the supercharger 44 in the intake passage 40 . EGR gas flowing through the EGR passage 52 enters an upstream portion of the supercharger 44 in the intake passage 40 without passing through the air bypass valve 48 of the bypass passage 47 .

A water-cooled EGR cooler 53 is arranged in the EGR passage 52 . The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also arranged in the EGR passage 52 . The EGR valve 54 adjusts the flow rate of exhaust gas flowing through the EGR passage 52 . By adjusting the opening of the EGR valve 54, the recirculation amount of the cooled exhaust gas, that is, the external EGR gas can be adjusted.

In this configuration example, the EGR system 55 is composed of an external EGR system and an internal EGR system. The external EGR system can supply cooler exhaust gas to the combustion chamber 17 than the internal EGR system.

1 and 3, reference numeral 57 denotes an alternator 57 connected to the crankshaft 15. As shown in FIG. Alternator 57 is driven by engine 1 .

The engine combustion control device includes an ECU (Engine Control Unit) 10 for operating the engine 1 . The ECU 10 is a well-known microcomputer-based controller, and as shown in FIG. (Read Only Memory) for storing programs and data, and an input/output bus 103 for inputting/outputting electrical signals. The ECU 10 is an example of a control section.

Various sensors SW1 to SW17 are connected to the ECU 10 as shown in FIGS. The sensors SW1 to SW17 output signals to the ECU 10. FIG. The sensors include the following sensors.

Airflow sensor SW1: arranged downstream of the air cleaner 41 in the intake passage 40, and measures the flow rate of fresh air flowing through the intake passage 40. First intake air temperature sensor SW2: arranged downstream of the air cleaner 41 in the intake passage 40, and , to measure the temperature of fresh air flowing through the intake passage 40. First pressure sensor SW3: arranged downstream of the connecting position of the EGR passage 52 in the intake passage 40 and upstream of the supercharger 44, and Second intake air temperature sensor SW4: arranged downstream of the turbocharger 44 in the intake passage 40 and upstream of the connecting position of the bypass passage 47, and flows out of the turbocharger 44 Second pressure sensor SW5 for measuring gas temperature Second pressure sensor SW5: Attached to surge tank 42 for measuring pressure of gas downstream of supercharger 44 In-cylinder pressure sensor SW6: Attached to cylinder head 13 corresponding to each cylinder 11 and measures the pressure in each combustion chamber 17 Exhaust temperature sensor SW7: Located in the exhaust passage 50 and measures the temperature of the exhaust gas discharged from the combustion chamber 17 Linear _O2 sensor SW8: Upstream in the exhaust passage 50 Lambda _O2 sensor SW9: Located downstream of the three-way catalyst 511 in the upstream catalytic converter and measures the oxygen concentration in the exhaust gas Water temperature sensor SW10: Attached to the engine 1 to measure the temperature of cooling water Crank angle sensor SW11: Attached to the engine 1 to measure the rotation angle of the crankshaft 15 Accelerator opening sensor SW12: To the accelerator pedal mechanism Intake cam angle sensor SW13: attached to the engine 1 to measure the rotation angle of the intake camshaft Exhaust cam angle sensor SW14: attached to the engine 1 and measures the rotation angle of the exhaust camshaft EGR differential pressure sensor SW15: arranged in the EGR passage 52 and measures the differential pressure upstream and downstream of the EGR valve 54 Fuel pressure sensor SW16: common rail 64 of the fuel supply system 61 and measures the pressure of the fuel supplied to the injector 6. Third intake air temperature sensor SW17: Attached to the surge tank 42 and measures the temperature of the gas in the surge tank 42, in other words, the intake air introduced into the combustion chamber 17 measure the temperature of

The ECU 10 determines the operating state of the engine 1 based on the signals from these sensors SW1 to SW17, and calculates control amounts for each device according to predetermined control logic. The control logic is stored in memory 102 . The control logic includes using maps stored in memory 102 to compute target and/or control variables.

The ECU 100 transmits electric signals related to the calculated control amount to the injector 6, the spark plug 25, the electric intake S-VT 23, the electric exhaust S-VT 24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, the supercharger 44. , the electromagnetic clutch 45 , the air bypass valve 48 , the swirl control valve 56 and the alternator 57 .

For example, the ECU 10 sets the target torque of the engine 1 and determines the target supercharging pressure based on the signal from the accelerator opening sensor SW12 and the map. Then, the ECU 10 adjusts the opening degree of the air bypass valve 48 based on the target supercharging pressure and the differential pressure across the supercharger 44 obtained from the signals of the first pressure sensor SW3 and the second pressure sensor SW5. By performing feedback control, the supercharging pressure is brought to the target supercharging pressure.

Further, the ECU 10 sets a target EGR rate (that is, the ratio of EGR gas to all gas in the combustion chamber 17) based on the operating state of the engine 1 and the map. Then, the ECU 10 determines the target EGR gas amount based on the target EGR rate and the intake air amount based on the signal of the accelerator opening sensor SW12, and the differential pressure across the EGR valve 54 obtained from the signal of the EGR differential pressure sensor SW15. By performing feedback control for adjusting the opening degree of the EGR valve 54 based on , the amount of external EGR gas introduced into the combustion chamber 17 is made to match the target EGR gas amount.

Furthermore, the ECU 10 executes air-fuel ratio feedback control when a predetermined control condition is satisfied. Specifically, the ECU 10 controls the fuel injection of the injector 6 so that the air-fuel ratio of the air-fuel mixture becomes a desired value based on the oxygen concentration in the exhaust gas measured by the linear _O2 sensor SW8 and the lambda _O2 sensor SW9. Adjust quantity.

Other details of the control of the engine 1 by the ECU 10 will be described later.

(SPCCI combustion concept)
The main purpose of the engine 1 is to improve fuel efficiency and exhaust gas performance. In the self-ignition combustion, if the temperature in the combustion chamber 17 before the start of compression varies, the self-ignition timing changes greatly. Therefore, the engine 1 performs SPCCI combustion, which is a combination of SI combustion and CI combustion.

In the SPCCI combustion, the ignition plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17, and the air-fuel mixture undergoes SI combustion due to flame propagation, and the heat generated by the SI combustion causes the combustion in the combustion chamber 17. When the temperature rises and the pressure in the combustion chamber 17 rises due to flame propagation, the unburned air-fuel mixture undergoes self-ignition for CI combustion.

By adjusting the calorific value of SI combustion, it is possible to absorb temperature variations in the combustion chamber 17 before the start of compression. By adjusting the ignition timing by the ECU 10, the air-fuel mixture can be self-ignited at the target timing.

In SPCCI combustion, the heat release during SI combustion is milder than that during CI combustion. As illustrated in FIG. 4, the waveform of the heat release rate in SPCCI combustion has a rising slope smaller than that in the waveform of CI combustion. Further, the pressure fluctuation (dp/dθ) in the combustion chamber 17 is also gentler during SI combustion than during CI combustion.

When the unburned air-fuel mixture self-ignites after the start of SI combustion, the slope of the heat release rate waveform may change from small to large at the timing of self-ignition. The heat release rate waveform may have an inflection point X at the timing θci at which CI combustion starts.

After the start of CI combustion, SI combustion and CI combustion are performed in parallel. Since CI combustion generates more heat than SI combustion, the heat release rate is relatively high. However, since the CI combustion is performed after the top dead center of the compression stroke, the slope of the heat release rate waveform is prevented from becoming too large. The pressure fluctuation (dp/dθ) during CI combustion also becomes relatively mild.

Pressure fluctuation (dp/dθ) can be used as an index representing combustion noise. As described above, SPCCI combustion can reduce the pressure fluctuation (dp/dθ), so it is possible to avoid excessive combustion noise. Combustion noise of the engine 1 is suppressed below the permissible level.

The SPCCI combustion ends when the CI combustion ends. CI combustion has a shorter combustion period than SI combustion. The SPCCI combustion has an earlier combustion end timing than the SI combustion.

The heat release rate waveform of SPCCI combustion is formed such that the first heat release rate portion _QSI formed by SI combustion and the second heat release portion _QCI formed by CI combustion are continuous in this order. It is

Here, the SI rate is defined as a parameter that indicates the characteristics of SPCCI combustion. The SI rate is defined as an index related to the ratio of the amount of heat generated by SI combustion to the total amount of heat generated by SPCCI combustion. The SI rate is the heat quantity ratio generated by two combustions with different combustion modes. A high SI rate results in a high proportion of SI combustion, and a low SI rate results in a high proportion of CI combustion. The SI rate may be defined as the ratio of the amount of heat generated by SI combustion to the amount of heat generated by CI combustion. That is, in SPCCI combustion, the crank angle at which CI combustion starts is defined as the CI combustion start timing θci, and in the waveform ₈₀₁ shown in FIG. From the area Q _CI of the CI combustion on the side, the SI rate may be set to Q _SI /Q _CI .

(engine operating range)
FIG. 5 exemplifies a map related to control of the engine 1. As shown in FIG. The map is stored in the memory 102 of the ECU 10. FIG. A map 504 illustrated in FIG. 5 is a map when the engine 1 is warm.

The map 504 is defined by the load and speed of the engine 1 . The map 504 is roughly divided into three regions, depending on whether the load is high or low and whether the rotation speed is high or low. Specifically, the three regions are a low load region A1 that includes idling and spreads over low and medium speed regions, medium and high load regions A2, A3 and A4 in which the load is higher than the low load region A1, and a low load region A1. This is a high rotation area A5 in which the rotation speed is higher than the load area A1 and the medium and high load areas A2, A3, and A4. The middle and high load regions A2, A3, and A4 are also divided into a middle load region A2, a high load middle rotation region A3 in which the load is higher than that in the middle load region A2, and a high load low rotation region A3 in which the rotation speed is lower than that in the high load middle rotation region A3. It is divided into area A4.

Here, the low speed region, the middle speed region, and the high speed region are obtained by dividing the entire operating region of the engine 1 in the rotational speed direction into approximately three equal parts: the low speed region, the middle speed region, and the high speed region. , a low rotation area, a middle rotation area, and a high rotation area. In the example of FIG. 5, a rotation speed of less than N1 is low rotation, a rotation speed of N2 or more is high rotation, and a rotation speed of N1 or more and less than N2 is medium rotation. The rotation speed N1 may be, for example, about 1200 rpm, and the rotation speed N2 may be, for example, about 4000 rpm.

Also, the low load range may be a range including a light load operating state, the high load range may be a range including a fully open load operating state, and the medium load may be a range between the low load range and the high load range. In addition, the low load range, the medium load range, and the high load range each divide the entire operating range of the engine 1 in the load direction into approximately three equal parts: the low load range, the medium load range, and the high load range. A low load range, a medium load range, and a high load range may also be used.

A map 504 in FIG. 5 indicates the state of the air-fuel mixture and the combustion mode in each region. The map 504 of FIG. 5 also indicates the driven and non-driven regions of the supercharger 44 . The engine 1 performs SPCCI combustion in a low load range A1, a medium load range A2, a high load medium speed range A3, and a high load low speed range A4. The engine 1 also performs SI combustion in other regions, specifically in the high revolution region A5.

(Engine operation in each area)
Operation of the engine 1 in each area of the map 504 of FIG. 5 will be described in detail below.

(Low load area)
When the engine 1 is operating in the low load region A1, the engine 1 performs SPCCI combustion.

The EGR system 55 introduces EGR gas into the combustion chamber 17 in order to improve fuel efficiency of the engine 1 . Specifically, the electric intake S-VT 23 and the electric exhaust S-VT 24 provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened near exhaust top dead center.

Also, the swirl generator forms a strong swirl flow in the combustion chamber 17 . The swirl control valve 56 is fully closed or has a predetermined degree of opening on the closing side. When a strong swirl flow is generated in the combustion chamber 17, the swirl flow is strong in the outer peripheral portion of the combustion chamber 17, while the swirl flow in the central portion is relatively weak. The injector 6 injects fuel into the combustion chamber 17 in which a strong swirl flow is formed, so that the air-fuel mixture in the central portion of the combustion chamber 17 is relatively rich in fuel, and the air-fuel mixture in the outer peripheral portion is relatively fuel-rich. Leaning, the mixture can be stratified.

The injector 6 injects fuel into the combustion chamber 17 multiple times during the intake stroke. The multiple fuel injections and the swirl flow in the combustion chamber 17 stratify the air-fuel mixture.

The air-fuel ratio (A/F) of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio throughout the combustion chamber 17 (that is, excess air ratio λ>1). More specifically, the A/F of the air-fuel mixture in the entire combustion chamber 17 is 25 or more and 31 or less. By doing so, the generation of RawNOx can be suppressed, and the exhaust gas performance can be improved.

After the end of fuel injection, the ignition plug 25 ignites the air-fuel mixture in the central portion of the combustion chamber 17 at a predetermined timing before the compression top dead center. The ignition timing may be the end of the compression stroke. The final stage of the compression stroke may be the final stage when the compression stroke is divided into three equal parts, the initial stage, the middle stage, and the final stage.

(medium and high load area)
Even when the engine 1 is operating in the middle and high load ranges A2 to A4, the engine 1 performs SPCCI combustion as in the low load range A1.

EGR system 55 introduces EGR gases into combustion chamber 17 . Specifically, the electric intake S-VT 23 and the electric exhaust S-VT 24 provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened near exhaust top dead center. Internal EGR gases are introduced into the combustion chamber 17 . Also, the EGR system 55 introduces the exhaust gas cooled by the EGR cooler 53 into the combustion chamber 17 through the EGR passage 52 . That is, the external EGR gas having a lower temperature than the internal EGR gas is introduced into the combustion chamber 17 . External EGR gas regulates the temperature in combustion chamber 17 to a suitable temperature. The EGR system 55 reduces the amount of EGR gas as the load on the engine 1 increases. The EGR system 55 may null EGR gases, including internal EGR gases and external EGR gases, at full load.

The air-fuel ratio (A/F) of the air-fuel mixture in the entire combustion chamber 17 is the stoichiometric air-fuel ratio (A/F≈14.7). By purifying the exhaust gas discharged from the combustion chamber 17 by the three-way catalysts 511 and 513, the exhaust gas performance of the engine 1 is improved. The A/F of the air-fuel mixture should be kept within the purification window of the three-way catalyst. The excess air ratio λ of the mixture may be 1.0±0.2. When the engine 1 is operating in the high-load medium-speed region A3 including full load (that is, maximum load), the A/F of the air-fuel mixture is the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio in the entire combustion chamber 17. It may be made richer than the air-fuel ratio (that is, the excess air ratio λ of the air-fuel mixture is λ≦1).

Since the EGR gas is introduced into the combustion chamber 17, G/F, which is the weight ratio of the total gas and fuel in the combustion chamber 17, becomes leaner than the stoichiometric air-fuel ratio. The G/F of the air-fuel mixture may be 18 or more. By doing so, it is possible to suppress the occurrence of so-called knocking. G/F may be set at 18 or more and 30 or less. Also, G/F may be set at 18 or more and 50 or less.

When the load of the engine 1 is medium load, the injector 6 performs fuel injection multiple times during the intake stroke. The injector 6 may perform the first injection in the first half of the intake stroke and the second injection in the second half of the intake stroke.

Further, when the load of the engine 1 is high, the injector 6 injects fuel during the intake stroke.

The spark plug 25 ignites the air-fuel mixture at a predetermined timing near the compression top dead center after the fuel is injected. When the load of the engine 1 is medium load, the spark plug 25 may ignite before the compression top dead center. When the load of the engine 1 is high, the spark plug 25 may ignite after the compression top dead center.

(Operation of supercharger)
Here, as shown in the map 504 of FIG. 5, the supercharger 44 is off (see S/C OFF) in a portion of the low load region A1 and a portion of the middle and high load region A2. Specifically, the supercharger 44 is off in the low-rotation-side region of the low-load region A1. In the low-load region A1 on the high rotation side, the supercharger 44 is turned on in order to ensure the necessary intake charge amount in response to the increase in the rotation speed of the engine 1 . In addition, the supercharger 44 is off in a part of the low-load, low-rotation side of the middle-to-high load range A2. In the high load region of the medium and high load region A2, the supercharger 44 is turned on in order to secure the required intake charge amount in response to the increase in the fuel injection amount. In addition, the supercharger 44 is also on in the high-rotation-side region in the middle-high load region A2.

Note that the supercharger 44 is on throughout the high load medium speed region A3, the high load low speed region A4, and the high speed speed region A5 (see S/C ON).

(high rotation area)
When the rotation speed of the engine 1 is high, the time required for the crank angle to change by 1° is shortened. It becomes difficult to stratify the air-fuel mixture in the combustion chamber 17 . When the rotation speed of the engine 1 increases, it becomes difficult to perform SPCCI combustion.

Therefore, when the engine 1 is operating in the high speed region A5, the engine 1 performs SI combustion instead of SPCCI combustion. Note that the high rotation region A5 extends over the entire load direction from low load to high load.

EGR system 55 introduces EGR gases into combustion chamber 17 . EGR system 55 reduces the amount of EGR gas as the load increases. The EGR system 55 may zero EGR gas at full load.

Swirl control valve 56 is fully open. A swirl flow is not generated in the combustion chamber 17, and only a tumble flow is generated. By fully opening the swirl control valve 56, it is possible to improve charging efficiency and reduce pump loss.

The air-fuel ratio (A/F) of the air-fuel mixture is basically the stoichiometric air-fuel ratio (A/F≈14.7) in the entire combustion chamber 17 . The excess air ratio λ of the air-fuel mixture may be set to 1.0±0.2. The excess air ratio λ of the air-fuel mixture may be less than 1 when the engine 1 is operating near a fully open load.

The injector 6 starts fuel injection during the intake stroke. The injector 6 injects fuel all at once. A homogeneous or substantially homogeneous mixture is formed in the combustion chamber 17 by initiating fuel injection during the intake stroke. In addition, since it is possible to secure a long vaporization time of the fuel, it is possible to reduce the unburned loss.

The spark plug 25 ignites the air-fuel mixture at an appropriate timing after the end of fuel injection and before the compression top dead center.

(Engine basic control)
FIG. 6 shows a flow of basic control of the engine 1 executed by the ECU 10. As shown in FIG. The ECU 10 operates the engine 1 according to control logic stored in the memory 102 . Specifically, the ECU 10 determines the operating state of the engine 1 based on the signals from the sensors SW1 to SW17, sets a target torque, and adjusts the torque in the combustion chamber 17 so that the engine 1 outputs the target torque. Calculations for adjusting the state quantity, adjusting the injection amount, adjusting the injection timing, and adjusting the ignition timing are performed.

When performing SPCCI combustion, the ECU 10 also controls the SPCCI combustion using two parameters, the SI rate and θci. Specifically, the ECU 10 determines a target SI rate and a target θci corresponding to the operating state of the engine 1, and controls the combustion chamber 17 so that the actual SI rate matches the target SI rate and the actual θci becomes the target θci. It adjusts the internal temperature and adjusts the ignition timing. The ECU 10 sets the target SI rate low when the load on the engine 1 is low, and sets the target SI rate high when the load on the engine 1 is high. When the load of the engine 1 is low, by increasing the proportion of CI combustion in SPCCI combustion, both suppression of combustion noise and improvement of fuel efficiency can be achieved. When the load of the engine 1 is high, increasing the proportion of SI combustion in SPCCI combustion is advantageous for suppressing combustion noise.

In step S121 of the flow of FIG. 6, the ECU 10 reads signals from the sensors SW1 to SW17, and in subsequent step S122, the ECU 10 sets the target acceleration based on the accelerator opening. In step S123, the ECU 10 sets a target torque required to achieve the set target acceleration.

In step S124, the ECU 10 determines the operating state of the engine 1, and determines whether the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio (that is, the excess air ratio λ=1). . If λ=1, the process proceeds to step S125, and if λ≠1, the process proceeds to step S129.

Steps S125 to S128 set control target values for each device when the engine 1 is operated in the middle load region A2, the high load middle speed region A3, the high load low speed region A4, and the high speed region A5. corresponds to the step of In step S125, the ECU 10 sets the target ignition timing of the spark plug 25 based on the set target torque. In subsequent step S126, the ECU 10 sets a target air amount to fill the combustion chamber 17 based on the set target torque. In step S127, the ECU 10 sets the target injection amount of fuel based on the set target air amount so that the air-fuel ratio of the air-fuel mixture becomes the stoichiometric air-fuel ratio or approximately the stoichiometric air-fuel ratio. Then, in step S128, the ECU 10 sets the target throttle opening of the throttle valve 43, the target SCV opening of the swirl control valve 56, the target EGR valve opening of the EGR valve 54, and the intake air amount based on the set target air amount. A target S-VT phase of the electric S-VT 23 and a target S-VT phase of the exhaust electric S-VT 24 are set.

Steps S129 to S1212 correspond to steps for setting control target values for each device when the engine 1 operates in the low load region A1. In step S129, the ECU 10 sets the target ignition timing of the spark plug 25 based on the set target torque. In subsequent step S1210, the ECU 10 sets the target injection amount of fuel based on the set target torque. In step S1211, the ECU 10 sets the target air amount to fill the combustion chamber 17 based on the set target injection amount so that the air-fuel ratio of the air-fuel mixture becomes a predetermined lean air-fuel ratio. The air-fuel ratio of the air-fuel mixture is between 25 and 31 as described above. Then, in step S1212, the ECU 10 sets the target throttle opening of the throttle valve 43, the target SCV opening of the swirl control valve 56, the target EGR valve opening of the EGR valve 54, and the intake air amount based on the set target air amount. A target S-VT phase of the electric S-VT 23 and a target S-VT phase of the exhaust electric S-VT 24 are set.

In step S1213, the ECU 10 adjusts the throttle opening of the throttle valve 43, the SCV opening of the swirl control valve 56, the EGR valve opening of the EGR valve 54, and the intake The S-VT phase of the electric S-VT 23 and the S-VT phase of the exhaust electric S-VT 24 are adjusted.

In step S1214, the ECU 10 causes the injector 6 to inject fuel at a predetermined timing according to the set target injection amount. In subsequent step S1215, the ECU 10 causes the ignition plug 25 to perform ignition at the set target ignition timing. Setting of the target ignition timing will be described later.

(Setting of target ignition timing)
In SPCCI combustion and SI combustion, when the ignition timing of the spark plug 25 is advanced, the timing at which the air-fuel mixture is burned advances. Advancement of the combustion timing is advantageous for improving the thermal efficiency of the engine 1 .

In SPCCI combustion, the proportion of CI combustion increases as the ignition timing is advanced. Combustion noise increases as the proportion of CI combustion in SPCCI combustion increases. Further, if the ignition timing is advanced too much, abnormal combustion may occur, which may reduce the reliability of the engine. Therefore, when performing SPCCI combustion, the ECU 10 advances the ignition timing within a range in which the combustion noise index falls within the allowable value.

In the SPCCI combustion, as described above, the spark plug 25 is ignited so that a portion of the air-fuel mixture begins to burn with flame propagation, and then the remaining air-fuel mixture burns due to self-ignition. In SPCCI combustion, the period from the ignition timing to the start of self-ignition varies depending on the state inside the combustion chamber 17 and the like. In SPCCI combustion, even if the ignition timing is the same, the combustion waveform may change. SPCCI combustion has a low correlation between ignition timing and cplf, which is a combustion noise index.

FIG. 7 illustrates the relationship between mfb50 and cplf. SPCCI combustion has a high correlation between mfb50 and cplf. That is, when mfb50 advances, cplf increases.

Combustion such that mfb50 is too slow, the air-fuel mixture does not initiate combustion by auto-ignition, but only burns by flame propagation (SI combustion). When mfb 50 advances, the air-fuel mixture begins to self-ignite. That is, the air-fuel mixture is SPCCI-burned. When the air-fuel mixture performs SPCCI combustion, the most retarded position of mfb50 is determined according to the state in the combustion chamber 17 (self-ignition mfb50 (most retarded angle)). Combustion with mfb50 later than the most retarded position is only SI combustion in which combustion by self-ignition does not start. The most retarded position of mfb 50 changes when the state of the combustion chamber 17 changes (see the dashed arrow in FIG. 7).

When the air-fuel mixture undergoes SI combustion, the amount of increase in cplf relative to the advance amount of mfb50 is relatively small. That is, the slope of the straight line to the right of the most retarded position of mfb 50 shown in FIG. 7 is small. CI combustion produces more combustion noise than SI combustion. When the air-fuel mixture undergoes SPCCI combustion, the amount of increase in cplf relative to the advance amount of mfb50 is relatively large. That is, the slope of the straight line to the left of the most retarded position of mfb 50 shown in FIG. 7 is large. SPCCI combustion differs from SI combustion in characteristics regarding combustion noise.

The dashed line in FIG. 7 illustrates the limiting value of cplf. The limit value of cplf is determined based on the running speed of the vehicle, the number of rotations of the engine 1, the load, etc., taking into consideration the marketability.

mfb50 can be advanced within a range not exceeding the limit value of cplf. For example, the intersection of the solid line and the dashed line in FIG. 7 can be set as the target value of mfb50. Once the target value of mfb50 is determined, the ECU 10 can determine the ignition timing so that mfb50 becomes the target value.

FIG. 8 shows the configuration of functional blocks of the ECU 10. As shown in FIG. The functional blocks shown in FIG. 8 relate to setting the ignition timing. The functional blocks include a cplf target value setting unit 10a, an mfb50 estimation unit 10b, a cplf estimation unit 10c, a target mfb50 calculation unit 10d, an ignition timing setting unit 10e, a CI influence ratio calculation unit 10f, a cplf calculation unit 10g, and an mfb50 calculation unit 10h. contains.

The cplf target value setting unit 10a, the mfb50 estimation unit 10b, the cplf estimation unit 10c, the target mfb50 calculation unit 10d, and the ignition timing setting unit 10e are functional blocks that set the ignition timing based on the measurement signals of the sensors SW1 to SW17. be. These functional blocks set the ignition timing by feedforward control.

The CI influence ratio calculation unit 10f, the cplf calculation unit 10g, and the mfb50 calculation unit 10h are functional blocks that correct models and relational expressions, which will be described later, based on the measurement signal of the in-cylinder pressure sensor SW6. These functional blocks are involved in setting the ignition timing through feedback control.

The cplf target value setting unit 10a sets the cplf target value from the cplf limit value. The cplf target value setting unit 10a sets the limit value of the cplf based on the traveling speed of the vehicle, the rotation speed of the engine 1, the load, etc. obtained from the measurement signals of the sensors SW1 to SW17, as described above. The cplf target value setting unit 10a sets the cplf target value from the cplf limit value. Specifically, as shown in FIG. 9, the cplf target value setting unit 10a sets the target value of cplf to Set to a value smaller than the limit value (see white arrow in FIG. 9). Specifically, the cplf target value setting unit 10a uses the standard deviation of cplf based on the cplf measurement data accumulated so far to set the target value of cplf so that the limit value of cplf is, for example, 3σ. stipulate.

The mfb50 estimator 10b estimates the most retarded position of mfb50 described above. Specifically, the mfb 50 estimator 10 b estimates the most retarded position of the mfb 50 based on the self-ignition model of the air-fuel mixture and the relational expression of the pressure change in the combustion chamber 17 .

A self-ignition model of air-fuel mixture is represented by Equation (1). The autoignition model is a model formula based on the Arrhenius formula.

T _CI ^A × P _CI ^B × (O2_rate) ^C × φ ^D /time = 1 (1)
However, T _CI is the temperature in the combustion chamber 17 when the air-fuel mixture self-ignites, _PCI is the pressure in the combustion chamber 17 when the air-fuel mixture self-ignites, O2_rate is the oxygen concentration in the combustion chamber 17, and φ is The equivalence ratio of the air-fuel mixture, time is time, and A, B, C, and D are constants.

O2_rate is determined based on the amounts of fresh air and EGR gas introduced into the combustion chamber 17 . φ is determined based on the amounts of fresh air, EGR gas, and fuel introduced into the combustion chamber 17 . time is determined from the number of revolutions of the engine 1 .

A relational expression of the pressure change in the combustion chamber is represented by Equation (2).

_PCI = P _BDC × (V _BDC /V _CI ) ^κ + Q × (κ - 1) / V _CI … (2)
However, P _BDC is the pressure in the combustion chamber at intake bottom dead center, V _BDC is the volume in the combustion chamber at intake bottom dead center, V _CI is the volume in the combustion chamber when the air-fuel mixture self-ignites, and Q is the air-fuel mixture. is the specific heat ratio of the air-fuel mixture. P _BDC is determined based on the measurement signal of the second pressure sensor SW5 attached to the surge tank 42 . Q is determined from a combustion model stored in the ECU 10. κ is determined based on the gas composition within the combustion chamber 17 .

The mfb 50 estimating unit 10b estimates the volume V _CI of the combustion chamber 17 at the time when the air-fuel mixture in the combustion chamber 17 starts self-ignition from equations (1) and (2). When estimating _VCI , for example, first-order approximation may be used.

By estimating the volume _VCI , the combustion waveform of the SPCCI combustion can be determined. Once the combustion waveform is determined, mfb50 is determined. That is, the mfb50 estimation unit 10b estimates the volume V _CI and estimates mfb50 from the estimated volume V _CI . The estimated mfb50 is the most retarded position of mfb50 when the air-fuel mixture performs SPCCI combustion (see self-ignition mfb50 (most retarded angle) in the upper diagram 91 of FIG. 9).

The cplf estimator 10c estimates the cplf at the most retarded position of mfb50 estimated by the mfb50 estimator 10b (see "estimated cplf" in the upper diagram 91 of FIG. 9). Combustion at the most retarded position of mfb50 is combustion with a small amount of CI combustion in SPCCI combustion. The cplf during combustion at the most retarded position of mfb50 can be estimated on the assumption that the air-fuel mixture undergoes SI combustion instead of SPCCI combustion. The cplf estimator 10c calculates the cplf during SI combustion based on the combustion waveform during SI combustion. A combustion waveform during SI combustion can be obtained, for example, by simulation or from actual combustion data. More specifically, cplf has a high correlation with the pressure change (dp/dt) inside the combustion chamber 17 . Therefore, the cplf estimator 10c determines the rate of change of heat release Q in the interval between mfb10 and mfb50 during SI combustion ((0.5Q-0.1Q)/(mfb50-mfb10)), the volume V of the combustion chamber 17, dp/dt is calculated from the time based on the engine speed, and cplf is estimated from the calculated dp/dt.

The target mfb50 calculation unit 10d calculates the target value of mfb50 based on the target value of cplf set by the target cplf value setting unit 10a and the cplf at the most retarded position of mfb50 estimated by the cplf estimation unit 10c. The target mfb50 calculator 10d calculates an advance angle amount by which mfb50 can be advanced with respect to the most retarded position of mfb50.

As described above, cplf has a high correlation with the pressure change (dp/dt) inside the combustion chamber 17 . When mfb50 advances, the volume of the combustion chamber 17 at the time of mfb50 decreases, and the pressure change in the combustion chamber 17 also increases. Therefore, the ratio of the volume of the combustion chamber 17 at mfb50 in combustion in which mfb50 is advanced from the most retarded position to the volume of the combustion chamber 17 at mfb50 at the most retarded position (hereinafter referred to as volume ratio) , and cplf, there is a correlation as shown in the lower diagram 92 of FIG. That is, the smaller the volume ratio, the larger the cplf. Note that the correlation between the volume ratio and cplf changes according to the most retarded angle position of mfb50. That is, the slope of the straight line in the lower diagram 92 of FIG. 9 changes according to the most retarded angle position of mfb 50 .

The target mfb50 calculation unit 10d calculates a volume ratio that satisfies the target value of cplf, as indicated by the solid arrow in FIG. 9, based on the target value of cplf, the estimated cplf, and the volume ratio. The target mfb50 calculator 10d converts the volume ratio into a target mfb50.

Note that the relationship between mfb50 and cplf in the upper diagram 91 of FIG. The target value of cplf may be calculated based on the relationship between and. In the following, the relationship between mfb50 and cplf is preset as the mfb50-cplf model. The ECU 10 stores the mfb50-cplf model (see FIG. 13).

Based on the target value of mfb50 calculated by the target mfb50 calculation unit 10d, the ignition timing setting unit 10e determines the ignition timing so that the combustion of the air-fuel mixture reaches the target mfb50. As the ignition timing advances, mfb50 also advances. The ignition timing setting unit 10e outputs an ignition signal to the ignition plug 25 according to the set ignition timing.

The CI influence ratio calculator 10f determines whether the combustion in the combustion chamber 17 was SPCCI combustion or SI combustion, based on the measurement signal of the in-cylinder pressure sensor SW6. If the combustion is SPCCI combustion, the CI influence ratio calculator 10f also calculates the influence ratio of CI combustion in the combustion.

The upper diagram 111 in FIG. 10 shows the change in the heat release rate dq/dθ with respect to the crank angle (solid line) when the combustion is SPCCI combustion, and the change when the mixture does not self-ignite and the combustion is SI combustion. change in heat release rate dq/dθ with respect to crank angle (solid line and dashed line). The lower graph 112 of FIG. 10 shows the change in heat release Q with respect to the crank angle when the combustion is SPCCI combustion (solid line), and the change in heat release Q with respect to the crank angle when the combustion is SI combustion (solid line and one point). dashed line) and are exemplified.

In the SPCCI combustion, after combustion by flame propagation is started by ignition, the air-fuel mixture self-ignites at θci, and combustion by self-ignition is performed. As shown in the upper diagram 111 of FIG. 10, the waveform of the heat release rate (dq/dθ) in SPCCI combustion has a shape in which the heat release peaks due to SI combustion and the heat release peaks due to CI combustion are stacked. . As shown in the lower diagram 112 of FIG. 10, the change in heat release in SPCCI combustion changes in slope before θci and after θci.

The CI influence ratio calculation unit 10f calculates the slope of the heat release Q during the period from mfb10 to mfb50 and the slope of the heat release Q during the period from mfb10 to dq/dθmax (that is, the crank angle at which dq/dθ is maximized). is compared to determine whether the combustion in the combustion chamber 17 was SPCCI combustion or SI combustion.

The slope of heat release Q in the period from mfb10 to mfb50 is expressed by the following formula (3), and the slope of heat release Q in the period from mfb10 to dq/dθmax is expressed by the following formula (4).

((0.5Q-0.1Q)/(mfb50-mfb10)) …(3)
((dq/dθmaxQ-0.1Q)/(dq/dθmax-mfb10)) …(4)
In the case of SI combustion, the values of equations (3) and (4) are approximately equal. On the other hand, for SPCCI combustion, the value of equation (4) is greater than the value of equation (3).

The CI influence ratio calculation unit 10f calculates the ratio between the formula (3) and the formula (4) ((dq/dθmaxQ−0.1Q)/(dq/dθmax−mfb10))/((0.5Q−0.1Q)/(mfb50 -mfb10))
exceeds 1, it is determined that the combustion in the combustion chamber 17 was SPCCI combustion. Also, the larger the ratio, the greater the influence of the CI combustion on the SPCCI combustion by the CI influence ratio calculator 10f. The value of the ratio is the CI influence ratio indicating the influence of CI combustion on SPCCI combustion.

The cplf calculator 10g calculates an actual cplf (that is, a measured cplf, see FIG. 11) based on the measurement signal of the in-cylinder pressure sensor SW6 when the combustion in the combustion chamber 17 is SPCCI combustion. The calculated cplf is accumulated. Using the accumulated cplf, the standard deviation of the actual cplf is calculated. The standard deviation of the actual cplf is used to set the target value of cplf as described above.

The cplf calculator 10g also corrects the relationship between mfb50 and cplf (upper diagram 91 in FIG. 9), in other words, the relationship between the volume ratio and cplf (lower diagram 92 in FIG. 9), based on the measured cplf. Specifically, the cplf calculation unit 10g follows a procedure opposite to the procedure in which the target mfb50 calculation unit 10d calculates the target mfb50, and calculates mfb50 from the calculated actual cplf, the CI influence ratio, and the measured mfb10 and mfb50. cplf at the most retarded position is calculated (see arrow in FIG. 11). The cplf calculator 10g compares the cplf at the most retarded position of mfb 50 based on the actual measurement with the cplf at the most retarded position of mfb 50 estimated by the cplf estimator 10c. The cplf calculation unit 10g corrects the relationship between mfb50 and cplf, that is, the straight line 92 in the lower diagram of FIG. .

The mfb50 calculator 10h calculates the actual mfb50 (that is, the measured mfb50; see FIG. 11) based on the measurement signal of the in-cylinder pressure sensor SW6 when the combustion in the combustion chamber 17 is SPCCI combustion. The mfb50 calculator 10h also corrects the self-ignition model used in the mfb50 estimator 10b based on the calculated measured mfb50.

Correction of the autoignition model is performed by assuming that the deviation of mfb50 is caused by the deviation of the in-cylinder temperature, and correcting the temperature-related parameters of the autoignition model. Specifically, the mfb50 calculation unit 10h follows a procedure opposite to the procedure in which the target mfb50 calculation unit 10d calculates the target mfb50. Calculate the volume. The mfb50 calculation unit 10h solves the self-ignition model for temperature using the volume at the most retarded angle position of mfb50 based on the actual measurement value, and calculates the difference from the temperature at the most retarded angle position of mfb50 estimated by the mfb50 estimation unit 10b. , to reflect the autoignition model.

(Ignition control procedure)
FIG. 12 is a flowchart showing a procedure related to ignition control of the spark plug 25 executed by the ECU 10. As shown in FIG. In step S1 after the start, the ECU 10 reads detection signals from the sensors SW1 to SW17. After step S1, the ECU 10 executes the processes of steps S2 to S7 and the processes of steps S8 to S10 in parallel.

In step S2, the cplf target value setting unit 10a determines the cplf limit value based on the running state of the vehicle and/or the operating state of the engine 1, as described above. In subsequent step S3, the mfb 50 estimator 10b estimates the most retarded position of the mfb 50 when the air-fuel mixture undergoes SPCCI combustion, based on the autoignition model.

In step S4, the cplf estimation unit 10c estimates cplf at the most retarded position of mfb 50 estimated in step S3. In subsequent step S5, the cplf target value setting unit 10a sets the target value of cplf from the limit value of cplf set in step S2, and the target mfb50 calculation unit calculates the target value of cplf and the maximum value estimated in step S3. As described above, the target value of mfb50 is calculated from cplf at the retarded position.

In step S6, the ignition timing setting unit 10e sets the ignition timing from the target value of mfb50 calculated in step S5. Then, the ignition timing setting unit 10e outputs an ignition signal to the ignition plug 25 in step S7. The spark plug 25 ignites the air-fuel mixture in the combustion chamber 17 according to the ignition signal.

In step S8, the CI influence ratio calculation unit 10f determines whether or not the air-fuel mixture undergoes SPCCI combustion, and if SPCCI combustion occurs, calculates the CI influence ratio. In subsequent step S9, the mfb50 calculator 10h calculates the most retarded position of mfb50 from the CI influence ratio and mfb50 measured based on the measurement signal of the in-cylinder pressure sensor SW6. The ECU 10 corrects the self-ignition model based on the difference between the most retarded position of mfb 50 calculated in step S9 and the most retarded position of mfb 50 estimated in step S3.

In subsequent step S10, the cplf calculation unit 10g calculates the cplf at the most retarded position based on the cplf measured based on the measurement signal of the in-cylinder pressure sensor SW6, the CI influence ratio, and the measured mfb10 and mfb50. do. The ECU 10 corrects the relationship between the volume ratio and the cplf according to the difference between the cplf calculated in step S10 and the cplf estimated in step S4.

(Setting of target ignition timing corresponding to engine transient)
If the ignition timing is controlled according to the above-described logic, both suppression of combustion noise and improvement of fuel economy performance are achieved when the operating state of the engine is constant or substantially constant. However, when the operating state of the engine changes, the combustion noise may increase.

This problem is caused by setting the target value of cplf. That is, in the logic described above, the target value of cplf is determined using the standard deviation of the measured cplf so that the cplf does not exceed the limit value in consideration of the combustion variation (variation in combustion). Specifically, the target value of cplf is set such that the limit value of cplf is, for example, 3σ. Note that the cplf measurement data is subjected to low-pass filter processing for the purpose of noise removal and the like.

However, when the operating state of the engine 1 changes over time, the combustion fluctuation also changes from moment to moment as the operating condition of the engine 1 changes from moment to moment. The standard deviation of cplf also changes moment by moment when the engine 1 is in transition. The standard deviation of cplf based on low-pass filtered measurement data changes slowly over time. When the standard deviation of cplf based on the measurement data is used to determine the target value of cplf when the engine 1 is in transition, the target value of cplf greatly deviates from the operating state of the engine 1, and as a result, cplf is limited. exceed the value. That is, the combustion noise becomes louder.

Therefore, the cplf target value setting unit 10a predicts the standard deviation of cplf using a model, and determines the target value of cplf using the predicted standard deviation of cplf. As a result, cplf is prevented from exceeding the limit value both in the steady state and in the transient state of the engine 1 .

FIG. 13 illustrates the configuration of the cplf target value setting unit 10a. The cplf target value setting unit 10a corresponds to the cplf target value setting unit 10a shown in FIG. The cplf target value setting unit 10a has a cplf limit value setting unit 10a1, a first sigma calculation unit 10a2, a second sigma calculation unit 10a3, a filtering unit 10a4, and a correction unit 10a5.

As described above, the cplf limit value setting unit 10a1 sets the cplf limit value according to the operating state of the engine 1 (see the dashed line 141 in the upper diagram of FIG. 14).

The first sigma calculator 10a2 calculates the standard deviation of the actual cplf measured based on the measurement signal of the in-cylinder pressure sensor SW6. As described above, the cplf calculator 10g calculates the actual cplf based on the measurement signal of the in-cylinder pressure sensor SW6. The first sigma calculator 10a2 calculates and stores the standard deviation of the cplf based on the measured cplf.

The second sigma calculator 10a3 calculates the standard deviation of cplf using a model. Specifically, the second sigma calculation unit 10a3 calculates the standard deviation of cplf at the limit value of cplf based on the mfb50-sigma model and the mfb50-cplf model. The mfb50-sigma model represents the relationship between mfb50 and mfb50 variability. The mfb50-cplf model represents the relationship between mfb50 and cplf.

More specifically, as shown in the upper diagram 141 of FIG. 14, the second sigma calculator 10a3 calculates the cplf limit value from the cplf limit value set by the cplf limit value setting unit 10a1 and the mfb50-cplf model. Identify the corresponding mfb50. The second sigma calculator 10a3 also calculates the standard deviation of cplf equivalent to 1 sigma, the standard deviation of cplf equivalent to 2 sigma, and the standard deviation of cplf equivalent to 3 sigma of mfb50 corresponding to the cplf limit value, are calculated respectively. Then, the second sigma calculator 10a3 calculates the average value of the calculated standard deviation of the cplf equivalent to 1 sigma, the standard deviation of the cplf equivalent to 2 sigma, and the standard deviation of the cplf equivalent to 3 sigma, and calculates the limit value of the cplf as Let the standard deviation of cplf at The second sigma calculator 10a3 can accurately estimate the standard deviation σ of cplf at the limit value of cplf by using a model related to the variation of mfb50.

The filtering unit 10a4 calculates a first standard deviation without low-pass filtering and a second standard deviation with low-pass filtering for the standard deviation σ of cplf calculated by the second sigma calculating unit 10a3. .

FIG. 15 illustrates temporal changes in the standard deviation σ of cplf. The solid line in FIG. 15 is the change in the first standard deviation without low-pass filtering. In the example of FIG. 15, the engine 1 is in a steady state before time t1. Before time t1, the first standard deviation is constant or substantially constant. The period from time t1 to t2 is the transition period of the engine 1 . In the example of FIG. 15, the first standard deviation changes stepwise as the operating state of the engine 1 changes. The first standard deviation that is not filtered has high responsiveness to changes in the operating state of the engine 1 . After time t2, the engine 1 is in a steady state. The first standard deviation is constant or nearly constant.

The dashed line in FIG. 15 is the change in the second standard deviation after low-pass filtering. Before time t1, the second standard deviation is also constant or nearly constant and matches or nearly matches the first standard deviation. Even after time t2, the second standard deviation is constant or nearly constant and matches or nearly matches the first standard deviation.

Between times t1 and t2, the second standard deviation changes as the operating state of the engine 1 changes, but the change in the second standard deviation is slower than the change in the first standard deviation. The filtered second standard deviation has low responsiveness to changes in the operating state of the engine 1 . The dashed line in FIG. 15 corresponds to the change in the standard deviation of the measured cplf calculated by the first sigma calculator 10a2 based on the measurement signal of the in-cylinder pressure sensor SW6.

The correction unit 10a5 corrects the standard deviation of the measured cplf calculated by the first sigma calculation unit 10a2 based on the standard deviation of the cplf calculated by the second sigma calculation unit 10a3 using the model. Specifically, the correction unit 10a5 adds the difference Δσ (see FIG. 15) between the first standard deviation without low-pass filtering and the second standard deviation with low-pass filtering to the standard deviation of the measured cplf.

Before time t1 and after time t2, when the engine 1 is stationary, Δσ is zero or nearly zero. The correction unit 10a5 does not correct the standard deviation of the measured cplf calculated by the first sigma calculation unit 10a2. When the engine 1 is stationary, the correction unit 10a5 sets the target value from the limit value of cplf based on the standard deviation of the measured cplf, as shown in the upper diagram 91 of FIG.

On the other hand, since Δσ is not zero during the transition of the engine 1 between times t1 and t2, the correction unit 10a5 corrects the standard deviation of the measured cplf calculated by the first sigma calculation unit 10a2. When the engine 1 is in transition, the correction unit 10a5 adds Δσ to the standard deviation of the measured cplf and sets the target value from the limit value of the cplf as shown in the lower diagram 142 of FIG. arrow).

The correction unit 10a5 corrects the standard deviation of the measured cplf calculated by the first sigma calculation unit 10a2 based on the standard deviation of the cplf calculated by the second sigma calculation unit 10a3 using the model. Correction unit 10a5 feedforwards the standard deviation of cplf calculated using the model to the standard deviation of cplf calculated based on the measurement signal of in-cylinder pressure sensor SW6.

Since the corrected standard deviation of cplf represents the variation of cplf when the engine 1 is in transition, the cplf target value setting unit 10a can appropriately set the target value of cplf when the engine 1 is in transition. As a result, even when the engine 1 is in transition, cplf is suppressed from exceeding the limit value. For example, when the driver depresses the accelerator pedal, combustion noise is prevented from increasing significantly.

Further, even when the engine 1 is in transition, the mfb 50 is advanced to the extent possible, so the fuel consumption performance of the engine 1 is improved.

The cplf target value setting unit 10a does not determine whether the engine 1 is in a steady state or in a transient state. While the control logic of the engine 1 is simplified, the target value of cplf can be appropriately set in each of the steady state and the transient state of the engine 1 . Both suppression of combustion noise and improvement of fuel consumption performance are achieved.

Next, setting the ignition timing will be described with reference to the flow of FIG. The flow of FIG. 16 shows the calculation procedure of the target mfb50 in step S5 of the flow of FIG.

First, in step S51, the ECU 10 calculates mfb50 at the cplf limit value based on the most retarded position of mfb50, cplf at the most retarded position, and the cplf limit value when the air-fuel mixture performs SPCCI combustion. .

In subsequent step S52, the ECU 10 calculates the standard deviation of cplf corresponding to 1σ, 2σ, and 3σ of mfb50 at the cplf limit value. The ECU 10 also calculates the average of the calculated standard deviation of the cplf equivalent to 1σ, the standard deviation of the cplf equivalent to 2σ, and the standard deviation of the cplf equivalent to 3σ. Let it be the standard deviation of cplf.

In step S53, the ECU 10 calculates the difference Δσ between the first standard deviation without low-pass filtering and the second standard deviation with low-pass filtering for the standard deviation of cplf calculated in step S52. The standard deviation of cplf obtained from the measured value of the internal pressure sensor SW6 is corrected. As noted above, if Δσ is zero or near zero, the standard deviation of cplf is substantially uncorrected. If Δσ is non-zero, the standard deviation of cplf is corrected.

Then, in step S54, the ECU 10 sets the cplf target value based on the cplf limit value and the cplf standard deviation corrected in step S53. A target mfb50 is set from the target value and cplf at the most retarded position.

When the target mfb50 is set, the process proceeds to step S6 in the flow of FIG. 12, where the ignition timing is set and ignition is performed at the set ignition timing (step S7).

Note that the technology disclosed herein is not limited to application to the engine 1 having the configuration described above. Various configurations can be adopted for the configuration of the engine 1 .

1 engine 10 ECU (control unit)
10a cplf target value setting unit 10a2 first sigma calculation unit 10a3 second sigma calculation unit 10a5 correction unit 10b mfb50 estimation unit 10c cplf estimation unit 10d target mfb50 calculation unit 10e ignition timing setting unit 17 combustion chamber 25 spark plug (ignition unit)
SW1 Airflow sensor (measurement part)
SW2 1st intake air temperature sensor (measurement part)
SW3 1st pressure sensor (measurement part)
SW4 2nd intake air temperature sensor (measurement part)
SW5 2nd pressure sensor (measurement part)
SW6 In-cylinder pressure sensor (measurement part)
SW7 Exhaust temperature sensor (measurement part)
SW8 Linear _O2 sensor (measurement part)
SW9 Lambda _O2 sensor (measurement part)
SW10 water temperature sensor (measuring part)
SW11 Crank angle sensor (measurement part)
SW12 accelerator opening sensor (measurement part)
SW13 intake cam angle sensor (measurement part)
SW14 Exhaust cam angle sensor (measurement part)
SW15 EGR differential pressure sensor (measurement part)
SW16 Fuel pressure sensor (measurement part)
SW17 3rd intake air temperature sensor (measurement part)

Claims (5)

an ignition unit facing a combustion chamber of an engine mounted on an automobile and igniting an air-fuel mixture in the combustion chamber based on an ignition signal;
a measurement unit that outputs measurement signals of parameters related to the operation of the engine;
A control unit that receives a measurement signal from the measurement unit and performs calculation, and outputs an ignition signal based on the calculation result to the ignition unit,
The measurement unit includes a cylinder pressure sensor that outputs a measurement signal corresponding to pressure changes in the combustion chamber,
The control unit causes the ignition unit to perform partial self-ignition combustion in which the remaining mixture burns by self-ignition after a part of the mixture starts combustion with flame propagation by ignition of the ignition unit. outputting the ignition signal;
The control unit
a target value setting unit that sets a target value of the cplf from a limit value of the combustion noise index (cplf) set based on the measurement signal of the measurement unit;
an mfb50 estimating unit that estimates the most retarded position of the crank angle (mfb50 ) at which the mass combustion ratio is 50% when the air-fuel mixture performs partial self-ignition combustion based on the self-ignition model of the air-fuel mixture;
Combustion that satisfies the target value of cplf based on the target value of cplf set by the target value setting unit, the most retarded position of mfb50 estimated by the mfb50 estimation unit, and the predetermined relationship between mfb50 and cplf a target mfb50 calculator that calculates the mfb50 of
an ignition timing setting unit that sets an ignition timing that becomes the target mfb50 calculated by the target mfb50 calculation unit and outputs an ignition signal corresponding to the set ignition timing;
The target value setting unit
a first sigma calculator that calculates the standard deviation of the actual cplf based on the measurement signal of the in-cylinder pressure sensor;
Based on the mfb50-sigma model representing the relationship between mfb50 and mfb50 variation and the relationship between mfb50 and cplf, the standard deviation of cplf at the cplf limit from the mfb50 variation corresponding to the cplf limit a second sigma calculator that calculates
a correction unit that corrects the standard deviation of cplf calculated by the first sigma calculation unit based on the standard deviation of cplf calculated by the second sigma calculation unit;
The target value setting unit sets a target value of cplf based on the limit value of cplf and a corrected standard deviation of cplf so that cplf does not exceed the limit value.
In the engine control device according to claim 1,
The correction unit calculates the difference between the first standard deviation without low-pass filtering and the second standard deviation after low-pass filtering with respect to the standard deviation of cplf calculated by the second sigma calculation unit,
The correction unit adds a difference between the first standard deviation and the second standard deviation to the standard deviation of cplf calculated by the first sigma calculation unit. In the engine control device according to claim 1 or 2,
The second sigma calculator,
a standard deviation of cplf corresponding to 1 sigma of mfb50 corresponding to the cplf limit;
a standard deviation of cplf corresponding to 2 sigma of mfb50 corresponding to the cplf limit;
a standard deviation of cplf corresponding to the 3 sigma of mfb50 corresponding to the limit of cplf;
is the standard deviation of cplf at the limit value of cplf. In the engine control device according to any one of claims 1 to 3,
The control unit determines whether partial self-ignition combustion of the air-fuel mixture has occurred based on the measurement signal of the cylinder pressure sensor, and if partial self-ignition combustion has occurred, measurement of the cylinder pressure sensor is performed. An engine control device that corrects the relationship between the mfb 50 and cplf using the actual cplf measured based on the signal. In the engine control device according to any one of claims 1 to 4,
The mfb50 estimation unit
Self-ignition model of air-fuel mixture T _CI ^A ×P _CI ^B ×(O2_rate) ^C ×φ ^D /time=1
(However, T _CI is the temperature in the combustion chamber when the air-fuel mixture self-ignites, _PCI is the pressure in the combustion chamber when the air-fuel mixture self-ignites, O2_rate is the oxygen concentration in the combustion chamber, and φ is the equivalence ratio of the air-fuel mixture. , time is time, A, B, C, and D are constants), and
Relational expression of pressure change in the combustion chamber P _CI = P _BDC × (V _BDC /V _CI ) ^κ + Q × (κ - 1) / V _CI
(However, P _BDC is the pressure in the combustion chamber at intake bottom dead center, V _BDC is the volume in the combustion chamber at intake bottom dead center, V _CI is the volume in the combustion chamber when the mixture self-ignites, and Q is the mixture κ is the specific heat ratio of the air-fuel mixture)
, and estimates the most retarded position of mfb 50 from _{the estimated volume V CI of} the combustion chamber at the time when the air-fuel mixture in the combustion chamber starts self-ignition.

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